1. Field of the Invention
The present disclosure relates to the field of oil and gas exploration and production. More specifically, the present disclosure concerns a system and method for subterranean excavation for adjusting weight on bit based on monitoring wellbore fluid density changes.
2. Description of Related Art
Boreholes for producing hydrocarbons within a subterranean formation are generally formed by a drilling system employing a rotating bit on the lower end of a drill string. The drill string is suspended from a derrick which includes a stationary crown block assembly connected to a traveling block via a steel cable that allows movement between the two blocks. The drill string can be rotated by a top drive or Kelly above the borehole entrance. Drilling fluid is typically pumped through the drill string that then exits the drill bit and travels back to the surface in the annulus between the drill string and wellbore inner circumference. The drilling fluid maintains downhole pressure in the wellbore to prevent hydrocarbons from migrating out of the formation cools and lubricates the bit and drill string, cleans the bit and bottom hole, and lifts the cuttings from the borehole. The drilling bits are usually one of a roller cone bit or a fixed drag bit. Impactors have recently been developed for use in subterranean excavations. Conventionally impactors are injected into a pressurized circulation fluid to form a slurry. The slurry is then directed to a drill string, having a bit on its lower end, and discharged through nozzles on the bit to structurally alter the subterranean formation.
During excavation operations the drill bit applies an axial force to the formation, the axial force is typically referred to as weight on bit (WOB). The drill string is suspended by the block assembly. As the bit is lowered to the bottom of the hole, a portion of the drillstring's suspended load is transferred to compressional load. The compressional load is commonly referred to as the weight on bit (WOB). As the bit drills, the WOB is monitored by a weight on bit indicator at the surface and the drillstring is lowered to maintain compressional loading at the bit (or WOB) within predetermined limits. The WOB limits are dependent on a number of factors including: bit type, formation type and hardness, bottom hole assembly configuration, and desired results Additionally, adjusting the WOB may be necessary to maximize rate of penetration, especially when different formations are encountered. On the other hand, too much WOB can damage the bit, drill string, or other axial load bearing members.